Secunia

A vulnerability has been reported in Microsoft Windows, which can be exploited by malicious people to compromise a vulnerable system.

The vulnerability is caused due to a boundary error in the "CanonicalizePathName()" function in netapi32.dll and can be exploited to cause a stack-based buffer overflow via e.g. a malicious NetrpPathCanonicalize RPC request with an overly long path name to the Server Service (port 139/TCP or 445/TCP).

Successful exploitation allows execution of arbitrary code.

NOTE: According to Microsoft, the vulnerability is already being actively exploited.

Another unspecified issue discovered by Microsoft has also been reported.

Solution
Apply patches.
Further details available in Customer Area

Provided and/or discovered by
The vendor credits US-CERT and SANS.

Changelog
Further details available in Customer Area

Original Advisory
MS06-040 (KB921883):
http://www.microsoft.com/technet/security/Bulletin/MS06-040.mspx

Microsoft:
http://www.microsoft.com/technet/security/advisory/922437.mspx

Other references
Further details available in Customer Area

Deep Links
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